Wear-resistant cast iron for sliding surfaces

ABSTRACT

A wear-resistant and self-lubricatory cast iron for use with a compositely electroplated layer of a high wear resistance in sliding contact relation. The cast iron contains, in addition to carbon, silicon, manganese and chromium, cobalt for solid solubilization with the iron matrix and provision of high heat resistance, molybdenum and niobium for formation of such specific granular carbides as composite carbides of molybdenum and carbides of niobium and providing a high wear resistance, nickel for acceleration of graphitization and even distribution of fine and dense graphite in the iron matrix, and boron for aid of such acceleration in cooperation with the molybdenum thus providing high lubricity, the remainder being iron and impurities.

United States Patent 1 1 Kuriyama et a1.

1 Sept. 30, 1975 l l WEAR-RESISTANT CAST IRON FOR SLIDING SURFACES [73]Assignee: Suzuki Jidosha Kogyo Kabushiki Kaisha, Shizuoka-Prefecture,Japan [22} Filed: Oct. 29, 1974 [21] Appl, No.: 518,514

[30] Foreign Application Priority Data Nov. 1, 1973 Japan 48-123204 [52}U.S. Cl 1. 75/128 B; 75/123 CB; 75/128 C; 75/128 D; 75/128 F; 75/128 G;75/128 W [51] Int. Cl. ..C22C 38/44; C22C 34/48; C22C 38/52; C22C 38/56[58] Field of Search 75/128 D, 123 CB, 128 B, 75/128 C, 128 F, 128 G,128 W [56] References Cited UNlTED STATES PATENTS 3,658,515 4/1972Saltzman 75/128 C 3,767,386 10/1973 Ueda et a1. 75/123 CB 3,834,9019/1974 Kamiya et al.. 75/128 8 3,853,545 10/1974 Kusaka et a1 75/128 BPrimary Examiner-L. Dewayne Rutledge Assistant E.\'znniner-Arthur J1Steiner Attorney, Agent, or FirmJoseph P. Gastel l 57 ABSTRACT Awear-resistant and self-lubricatory cast iron for use with a compositelyelectroplated layer of a high wear resistance in sliding contactrelation. The cast iron contains, in addition to carbon, silicon,manganese and chromium, cobalt for solid solubilization with the ironmatrix and provision of high heat resistance, molybdenum and niobium forformation of such specific granular carbides as composite carbides ofmolybdenum and carbides of niobium and providing a high wear resistance,nickel for acceleration of graphitization and even distribution of fineand dense graphite in the iron matrix, and boron for aid of suchacceleration in cooperation with the molybdenum thus providing highlubricity, the remainder being iron and impuritics.

1 Claim, 8 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of23,909,252

FIG.

ABRASION VELOCITY (m/sec) ISTON MEASURING POSITIONS (8 POSITIONS MARKEDWITH ON CIRCUMFERE'NCE OF CIRCLE DEFINED BY A P AT TOP DEAD CENTER TOPDEAD CENTER" OF A PISTON WEAR-RESISTANT CAST IRON FOR SLIDING SURFACESBACKGROUND OF THE INVENTION The present invention relates to a metalmaterial for use in sliding contact with a metal surface coated with acompositely electroplated layer having a coprecipitated substanceprotruding above the electroplated metal surface.

Cast iron has heretofore been used as a metal material for use insliding contact with a metal surface coated with a compositelyelectroplated layer which has scaly graphite, granular graphite, orglobular graphite distributed through coprecipitation in uniform statetherein. Also, known is a metal material wherein, onto the surface of acast iron metal, molten molybdenum is sprayed, or hard chromium orbronze is electroplated. Such materials have their own respectiveproperties such as elastic modulus, deflection strength, hardness,impact resistance and fatigue limit stress, and considerations of suchindividual properties have inevitably forced one to compromise in theuse thereof for one purpose, since they have not completely satisfiedthe requirements in use throughout their properties. In other words,when a metal material of hard quality is used to mate with anelectroplated surface, the com positely electroplated surface in slidingcontact therewith is liable to wear readily. When a metal of softquality is used, the compositely electroplated surface is now relievedfrom such wear problem, but it is inevitable that the correspondingmaterial of soft quality is subject to wear and/or fusion seizure due toabrasion in operation, thus resulting in abnormal wear of the material.

In view of the above stated difficulties associated with theconventional metals for application to a corresponding part of amechanical structure which is adapted to slidably contact with acompositely electroplated surface as described above, it would beadvantageous if such a metal were to be developed which could be usedwith freedom from any possibility of abnormal phenomena describedhereinbefore. This invention is essentially directed toward meeting suchrequirements.

SUMMARY OF THE INVENTION It is therefore a primary object of thisinvention to provide a metal material providing a surface for slidingcontact with a compositely electroplated layer surface, and having asubstantial hardness whereby a positive resistance against wear due toabrasion is obtained.

It is another object of this invention to provide a metal materialproviding a porous surface which provides depressions for maintaininglubricant therein, whereby satisfactory lubrication may be assuredbetween the sliding contact surfaces of a mechanical structure.

It is still another object of this invention to provide a metal materialhaving a selfcontained lubricant in the surface thereof, wherebyscuffing and/or fusion seizure of the material due to abrasion with theassociated surface are effectively prevented.

It is a still further object of this invention to provide a practicablysuitable combination of a compositely electroplated layer with a castmetal, whereby hardness and lubricity provide an assurance of high wearresistance of the slidable contact metal members in a mechanicalstructure.

According to this invention, briefly summarized, there is provided animproved cast iron for use in sliding contact with a compositelyelectroplated layer in a mechanical structure, which contains 1.0 to 3.5percent of total carbon, 0.5 to 3.0 percent of silicon, 0.1 to 1.5percent of manganese, 0.1 to 2.0 percent of chromium, 1.0 to 15.0percent of cobalt, 0.5 to 10.0 percent of molybdenum, 0.1 to 5.0 percentof nickel, 0.05 to 2.0 percent of niobium, and 0.001 to 0.1 percent ofboron, the remainder being iron and impurities.

The foregoing objects, characteristics, principle, and utility of thepresent invention, as well as further objects and advantages thereof,will become more apparent from the following detailed description withrespect to a preferred embodiment of this invention when read inconjunction with the accompanying drawings, in which like parts aredesignated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 11 is an enlarged diagrammatic representation, in section, of acompositely electroplated layer adapted to serve as a sliding contactsurface of a mechanical structure;

FIG. 2 is a diagrammatic front elevation showing a wear tester;

FIG. 3 is a side elevation of the wear tester shown in FIG. 2;

FIG. 4 is a graphical representation showing the results of wear testsperformed by using the wear tester shown in FIGS. 2 and 3;

FIG. 5 is a side view, partly in longitudinal section, showing anultra-high-pressure wear tester;

FIG. 6 is a graphical representation showing the re sults of wear testsperformed by using the ultra-highpressure wear tester shown in FIG. 5;

FIG. 7 is an enlarged diagrammatic representation, in section, ofa castiron Z according to this invention; and

FIG. 8 is a schematic view showing positions for measuring averagequantity of abrasion observed in the case of Example 1.

DETAILED DESCRIPTION There have been proposed prior arts relating tocomposite electroplating as typically disclosed, for instance, by aJapanese Pat. No. 280939. According to this patent, there is disclosed amethod wherein there is electrolytically coprecipitated a composite filmconsisting of any one of metals such as nickel, chromium, copper,cadmium, and optionally selected powdered substances such as aluminumoxide, iron oxide, silicon carbide, tungsten carbide, diamond, etc. onthe surface of a metal matrix, thereby providing the metal surface withextraordinary resistance against wear, heat, corrosion, etc.. Amongthese substance applied in such com posite electrolytic operation, ithas been most common those skilled in the art to use nickel as ametallic component plus silicon carbide as a powdered admixture.

In this typical application, taken-by way of example from among otherknown arts, wherein a composite film is electroplated, an electrolyticbath containing nickel sulfamate, nickel chloride, boric acid and othereffective admixtures is first prepared in an electrolytic cell,thereafter powdered silicon carbide is further dispersed evenly to besuspended therein. In this particular electrolytic bath, it is essentialto use caution to keep the powdered substance admixed from settling inthe bath. Electrolytic nickel is used as anode and a metallic materialto be coated is used as cathode. With such arrangement, electrolyticoperation is performed by passing a current through the electrolyticcell and then coprecipitated on the surface of said material is powderedsilicon carbide to be evently dispersed in the electroplated layer ofnickel. In this electrolytic operation, silicon carbide as acoprecipitate is of a particle size of approximately 4 u, and thequantity of the silicon carbide to be coprecipitated in the compositelyelectroplated layer is approximately 6% by weight. Silicon carbide is amaterial having a knoop hardness of 2480, and, therefore, a compositelyelectroplated layer of high wear resistance can be produced bycoprecipitating silicon carbide in a nickel matrix. In practice, such anelectroplated layer may be applied to the interior wall surfaces of aninternal combustion engine cylinder, the sliding contact surfaces of amachine tool, the engaging surface of a clutch plate, and the like. Insuch an application, it is well known to those skilled in the art to usea compositely electroplated layer which has improved wear resistance, inthe following manner.

In the case of the interior wall surface of an internal combustionengine cylinder, for instance, wherein abrasion takes place on thecompositely electroplated layer thereof under wet conditions, there isprovided a sliding surface of porous character, which is available forcontaining a lubricant therein, whereby the lubricant may be suppliedincessantly onto the sliding surface of the engine cylinder, thuspreventing undesired abrasion from progressing. For this purpose, suchtreatment as electrolytic polishing, chemical polishing, and- /ormechanical polishing are applied to the compositely electroplated layerof nickel-silicon carbide. During this polishing treatment, nickel inthe compositely electroplated surface is subject to electrolyticdissolution, chemical dissolution, or mechanical dissolution, dependingon the polishing treatment referred to above.

In contrast, silicon carbide per se is not affected by such polishingtreatment and so remains in the compositely electroplated surface as itwas coprecipitated originally. Consequently, silicon carbide assumes astate of protrusion from the electroplated surface, the protrusionheight of such silicon carbide from above the surface of nickel matrixbeing of the order of l to 2 t. Thus, there are formed a first slidingcontact surface by silicon carbide particles per se and a second slidingcontact surface by the electroplated surface of the nickel matrix, thusforming spaces or depressions available for containing the lubricantbetween the first and second sliding contact surfaces. The thus obtainedsurface having silicon carbide particles protruding above the surface ofcompositely electroplated layer so as to form depressions available forcontaining the lubricant (hereinafter referred to as compositelyelectroplated surface) has a wear resistance superior to that obtainedin the conventional compositely electroplated layer.

In FIG. 1, there is shown an enlarged sectional view of a slidingsurface obtained by the above described composite electroplatingtechnique and comprising a first sliding contact surface 1, a secondsliding contact surface 2, and silicon carbide particles 4 protrudingfrom the surface of a nickel matrix 5, spaces or depressions forcontaining the lubricant being formed between the silicon carbideparticles and the two sliding contact surfaces.

Also, known is the use of cast iron as a metal material for a mechanicalpart corresponding, in cooperative sliding contact, to the abovementioned compositely electroplated layer surface. Cast iron has minordifferences in its physical properties according to the configurationand quality of graphite precipitated in the structure thereof. However,cast iron has been widely used in such application for the followingreasons. Graphite contained in the structure of cast iron has advantagessuch as its ability to store the lubricant so as to prevent theinterruption of the lubricant film and its own lubricity. Moreover, thedepressions from which graphite has come off become available forcontaining the lubricant, and, also, it can quickly dissipate frictionalheat by virtue of its high thermal conductivity and can fit byrunning-in against the contour of the electroplated member surface byvirtue of its low elastic modulus.

In the abrasion phenomenon observed in mechanical members in slidingcontact with each other, there are a so-called initial abrasion whichoccurs in the initial stage of use before the members become fittedsmoothly with each other, and normal abrasion which occurs in the normaloperation later than the above mentioned initial abrasion. It is knownthat a maximum quantity of wear is observed in such cases where thedirection of movement is reversed and/or a lubricant film isinterrupted. In this respect, it may be said that a material having thecapability of maintaining the lubricant and thus preventing theinterruption of a lubricant film can be considered to be a material ofgood wear resistance.

When the composite electroplating described hereinbefor is applied tothe cylinder interior wall surfaces of an internal combustion engine, itis required that piston rings to be set in cooperative sliding contactwith the above mentioned cylinder interior wall be of a metal materialhaving wear resistance as high as that of the compositely electroplatedlayer. Among cast iron materials for piston rings, a cast iron whereinthere are distributed much steadite of hard quality by increasingphosphorous in a pearlite matrix, and, further,

graphite globules are evenly distributed has advantages in wearresistance, heat resistance, and strength.

In the case where the above mentioned compositely electroplated layer iscaused to slide on the surface of a cast iron material, the surface of acast iron material is subject to scuffing and subsequent wear due toscratching by the hard silicon carbide particles protruding above thecompositely electroplated layer surface of the complementary member. Inthe interior wall of such cylinder coated with the compositelyelectroplated layer, there also occurs substantial wear particularly inpositions near the top and bottom dead centers of a piston, where thedirection of reciprocating movement of a piston is reversed, due to theinterruption of lubricant film therearound. For coping with suchproblems, there are such treatments as application of parkerizing,filling of solid lubricant, spraying of molten molybdenum,electroplating of such metals as hard chromium and copper, andelectroplating of bronze onto a copper and/or a chromium plated layer,but each treatment has advantages and disadvantages, and none of thesetreatments has been capable of solving the problems. For instance, hardchromium plating is on one hand selected for improving the wearresistance of such piston rings in view of the hardness thereof. On theother hand, however, there are drawbacks as that such hard chromiumplating is not readily run-in to fit the interior wall surface of acylinder, or the cylinder interior wall surface is subject tosubstantial wear. With respect to wear occurring on the part of castiron, one case is that wherein wear is caused by chemical componentscontained in the cast iron, and another is that wherein the cast ironitself wears physically. In Table 1, there are shown physical propertiesand chemical composition of such typical cast irons A, B, and C.

zation with the matrix of the cast iron. Furthermore, the addition ofmolybdenum and niobium into the cast iron results in the formation ofhard carbides of specific granular shape. In connection with theimprovement of self-lubricity thereof, the nickel therein serves as anaccelerator for the graphitization, while the boron and molybdenum causefine graphite particles to be distributed densely and evenly in thematrix, thus effecting such improvement. This cast iron Z has anunusually high elasticity which cannot be found in the conventional castirons, and specific granular carbides form a first sliding surface ofthis cast iron, thus resulting in superior wear resistance.

Table 1 Classification Elastic Chemical compositions (wt.%)

modulus Hardness Total Kind [Kg/mm Carbon Si Mn Cr Ni [H B 3.0 2.2 0.40.2 0.8 Cast lronA 11,000 108-114 3.5 2.8 -1.0 -0.4 12 Cast Iron B17,000 [H B] 3.5 2.2 0.5

[H C] 2.7 1.7 0.5 0.3 Cast Iron C 15,000 48 3.5 2.5 1.2 0.8

Classification Chemical composition (wt.

P S Mo V Cu Kind 0.3 0.05 0.8 0.05 Cast Iron A max max. 1.2 0.2

Cast Iron B max. max.

0.2 0.12 0.5 0.5 Cast Iron C 0.6 max. 1.0 1.0

In accordance with the present invention, there is provided a specialcast iron having a high wear resistance which is adaptable as a materialfor cast piston rings for sliding contact with the compositelyelectroplated layer described hereinbefore, and which is herein referredto as cast iron Z. The cast iron Z is processed in such an ordinarymanner where a cast iron is prepared, i.e., iron oxides of severaladditive elements, e.g., ferro-silicon, etc., are admixed to a moltengray cast iron. This cast iron has a number of advantages such asimproved hardness, heat resistance, and selflubricity over theconventional cast irons.

EXAMPLE 1 This example comprises an exemplary application of these castirons to piston rings for use in an air-cooled, two-stroke-cycle,internal combustion engine having a single cylinder for a motorcycle:

Table 2 Classification Elastic Chemical composition (wt. modulusHardness Total Kind [Kg/mm [H C] Carbon Si Mn Cr 1 .0 0.5 0.1 0.1 CastIron Z 20,000 36 38 3.5 3.5 1.5 2.0

Classification Chemical composition (wt. Co Mo Ni Nb B 1.0 0.5 0.1 0.050.001 Cast Iron Z Table 2 indicates certain physical properties and the65 In this example, the interior wall surface of the enchemicalcomposition of this cast iron Z. In this cast iron, cobalt added thereincontributes to the improve ment of heat resistance of the cast iron bysolid solubiligine cylinder having a bore x stroke of 56 mm X mm, and amaximum output of 10.2 HP/7,500 rpm is coated with a compositelyelectroplated layer of Ni-SiC :wuagzaz of the type described abovewherein SiC protrudes 1-2p. above the nickel. For the piston rings,those made of the conventional cast irons alone, the conventional castiron coated with a hard chromium layer, and the cast iron Z of thisinvention were prepared. The bench operation tests were performed for aperiod corresponding to a mileage of 2,000 km on road. After the testwas completed, wear at the points in the cylinder interior wall surfacecorresponding to the top dead center of the piston and the increase inthe gaps of the piston rings were measured thereby to judge theadaptability of the piston rings of such cast irons for use with thecompositely electroplated layer of the cylinder wall. The points of suchmeasurement in the cylinder interior wall surface corresponding to thetop dead center (top C.C.) of the piston were selected eight in numberpositioned equally spaced on the circumference of a circle defined onthe engine cylinder interior wall surface, which are schematically shownin FIG. 8. The results of the measurements of the average wear at theeight positions of the cylinder wall corresponding to the top deadcenter of the piston and increases in the gaps of the top piston ringand the second piston ring are indicated in Table 3.'

Table 3 Measured quantity Increase in Average wear Ring Gap at eightposi tions, top dead center Top ring 2nd ring Wear test by Ohkoshi typewear tester:

This type of wear tester is schematically shown in FIGS. 2 and 3. Inperforming a wear test with this wear tester, a rotor 8 of 30-mmdiameter covered with a compositely electroplated layer 7 was driven inrotation so as to slidably contact a fixed stator 9 under a load. Castirons A and Z were used as materials for the stator for the wear test.The results of the wear test were indicated in terms of the amount ofwear of the stator material. The conditions and results of this weartest are indicated in Table 4 and FIG. 4, respectively. The ordinate ofthe graph of FIG. 4 shows the volume of material in cubic millimeterswhich was removed during the wear test.

Lubricating oil Velocity of abrasion [m/sec] Distance of abrasionEXAMPLE 3 covered with a compositely electroplated layer 11 was fixedstationary under a load opposedly'against a jig with four statorpieces'l3' fixed rigidly thereto which was driven inrotation so as tocause the stator pieces to slidably contactthe stationary discfThereference numeral 14 designates a rotating shaft of a speed changer; 15designate's'an inlet for a lubricant, and 16 indicates the direction ofthe lubricant under pressure. The results of this wear test wereindicated in terms of roughness of a sliding surface for the compositelyelectroplated layer surface, while for the stator material the resultswere indicated in terms of height of wear loss after the performance ofthis test for a period corresponding to the running distance of 100 kmon the road. Comparison was made on the degree of wear by applying thesetest pieces for stator material of the cast iron A, the cast iron Asprayed with molten molybdenum, and the cast iron Z. The conditions andresults of the wear test are indicated in Table 5 and FIG. 6,respectively. The roughness or finishing degree of the compositelyelectroplated layer prior to the wear test was in the range of 0.6 to1.5 ;1..

Table 5 Method of abrasion Lubricated by Mobil No. 20,

oil temp. 60C, 600 cc/min Velocity of abrasion 3, 4, 5

[m/sec] Load of contact [kglcm Distance of abrasion I00 As for thephysical properties required by a metal material to be applied forsliding contact with a compositely electroplated layer surface, it isessential that it should not give rise to fusion seizure with theelectroplated surface, it should not scuff or scratch the electroplatedsurface, it should have a high wear resistance, etc. In Example 1, whenthe cast iron Z was used, no wear on the part of the compositelyelectroplated surface whatsoever was observed, and, furthermore, aslight increase in the gap of the piston rings was observed. In thisrespect, it can safely be said that the cast iron Z is amaterialsuitable for the manufacture of piston rings having good wear resistancefor use with a cylinder interior wall having a compositely electroplatedlayer.

Likewise in Example 2, it is apparent that the cast iron Z has greaterwear resistance than the conventional cast irons. It was found that thecast iron of Example 3 had no scuffing which was observed in the case ofthe cast iron A sprayed with molten molybdenum, and also was run-inappropriately to fit the compositely electroplated surface. In each ofthese examples, it was observed that the cast iron Z of this inventionhad good compatibility in associated use with the compositelyelectroplated layer of hard character.

Referring now to FIG. 7, there is diagrammatically shown asection of thecast iron Z of this invention showing the structure thereof. In FIG. 7,the reference numeral 18 designates a first sliding surface, 19 a secondsliding surface, 20 depressions containing the lubricant, 21 carbides 0fspecific granular shape, 22

graphite particles, and 23 the matrix of the cast iron Z.

These specific granular carbides are of hard molybdenum and niobium. Itshould be noted that the above mentioned specific granular carbides 21forming the first sliding surface 18 of the cast iron Z and the siliconcarbide 4 forming the first sliding surface 1 of the compositelyelectroplated surface of the corresponding part both have highhardnesses, and, in this respect, the cooperative use of such materialsfor sliding contact with each other becomes suitable for such purpose byvirtue of the outstandingly high wear resistance, thus affording gooddurability of such complementary parts of a mechanical structure.

Furthermore, as described hereinbefore, both the cast iron 2 and thecompositely electroplated layer have depressions 3 and 20 definedbetween the first and second sliding surfaces thereof, respectively, forcontaining the lubricant therein, thus supplying the lubricant containedtherein to the sliding surfaces of the complementary parts in slidingcontact with each other, and thus assuring the lubricity therebetween.Consequently, improved wear resistance of the two complementary parts isassured, and, simultaneously, quick running-in of the two is effected.Furthermore, as the cast iron Z has graphite 22 commixed therein as aself-contained lubricant, this graphite functions to prevent scuffingand/or fusion seizure of the two complementary parts. In this manner,there is now obtained an idealistic combination of metal materials foruse in sliding contact which solves all problems inherent in theconventional combination of metal materials for such use.

In summary, the advantageous features attained from the use, incombination, of the cast iron Z of this invention and the compositelyelectroplated layer are as follows:

1. By virtue of the first sliding surfaces formed by hard substances onthe both the compositely electroplated layer and the cast iron Z, highwear resistance is assured.

2. Because of depressions formed for containing the lubricant betweenthe first and second sliding surfaces on both the compositelyelectroplated layer and the cast iron Z, the lubricant is incessantlysupplied to the sliding surfaces thereof so as to assure lubricationtherebetween.

3. As a result of the existence of the first and second sliding surfacesof both the compositely electroplated layer and the cast iron Z, incooperation with depressions defined between these sliding surfaces, thecomplementary sliding parts are assured of quick running- 4. By virtueof self-contained lubricant of the case iron Z, there is no risk ofscuffing and/or fusion seizure of the associated surfaces of thecomplementary sliding parts.

What we claim is:

l. A cast iron for use in a sliding co ntact surface of a firstmechanical part adapted to cooperatively contact in sliding motion witha compositely electroplated layer wherein nickel and a silicon carbideare coprecipitated of a corresponding second mechanical part, said layerbeing subjected to surface treatment thereby to cause particles of saidsilicon carbide to protrude from above the surface of the nickelconstituting a matrix in said electroplated layer, said cast ironconsisting essentially of 1.0 to 3.5 percent of total carbon, 05 to 3.0percent of silicon, 0.1 to 1.5 percent of manganese, 0.1 to 2.0 percentof chromium, 1.0 to 15.0 percent of cobalt, 0.5 to 10.0 percent ofmolybdenum, 0.1 to 5.0 percent of nickel, 0.05 to 2.0 percent ofniobium, 0.001 to 0.1 percent of boron, and a remainder of iron andimpurities, all percentages being by weight.

1. A CAST IRON FOR USE IN A SLIDING CONTACT SURFACE OF A FIRSTMECHANICAL PART ADAPTED TO COOPERATIVELY CONTACT IN SLIDING MOTION WITHA COMPOSITELY ELECTROPLATED LAYER WHEREIN NICKEL AND A SILICON CARBIDEARE COPRECIPITATED OF A CORRESPONDING SECOND MECHANICAL PART, SAID LAYERBEING SUBJECTED TO SURFACE TREATMENT THEREBY TO CAUSE PARTICLES OF SAIDSILICON CARBIDE TO PRODUCE FROM ABOVE THE SURFACE OF THE NICKELCONSTITUTING A MATRIX IN SAID ELECTROPLATED LAYER, SAID CAST IRONCONSISTING ESSENTIALLY OF 1.0 TO 3.5 PERCENT OF TOTAL CARBON, 0.5 TO 3.0PERCENT OF SILICON, 0.1 TO 1.5 PERCENT OF MANGANESE, 0.1 TO 2.0 PERCENTOF CHORMIUM, 1.0 TO 15.0 PERCENT OF COBALT, 0.5 TO 10.0 PERCENT OFMOLYBDENUM, 0.1 TO 5.0 PERCENT OF NICKEL, 0.05 TO 2.0 PERCENT OFNIOBIUM, 0.001 TO 0.1 PERCENT PF BORON, AND A REMAINDER OF IRON ANDIMPURITIES ALL PERCENTAGES BEING BY WEIGHT.